Winding machines of the type used to build up large packages of synthetic filament yarns typically employ overhung or cantilever mandrels about which the yarns are wound as the mandrels rotate about their axes. Such machines will be referred to here at times as spooling frames and the yarn packages as spools. The cantilever or overhung type mounting for such a mandrel leaves on end of the mandrel free and accessible for the endwise insertion thereover of empty fiber (e.g. paper) tubes onto which the yarn may be wound and for the endwise removal therefrom of the full yarn packages formed as a result of the winding of the yarn onto the fiber tubes.
A contact roll ordinarily is disposed above the operative position of the mandrel on which the yarn packages are wound. Its mounting arrangement is such that it may move vertically as necessary in view of the changing diameter of the yarn packages as these are being built up. Means also are provided to press the contact roll downwardly to provide the desired contact with the peripheries of the yarn packages.
In some machines the contact roll is the driving roll for rotating the mandrel through friction with the yarn package on the mandrel. In other machines the contact roll is a speedometer roll which frictionally contacts the outer surface of the building yarn package to sense the peripheral speed thereof and provide an input signal for a drive for the mandrel. In all of these cases, however, it is desirable that the contact roll press with reasonable uniformity against substantially the entire length of all the yarn packages being wound on a mandrel at a given time
If only a single short spool or yarn package is built up on the spool mandrel, the pressing force can be kept within the desired limits by well-known means. Here, the small differences in parallelism between the mandrel and the contact roll which arise as the yarn package builds up do not greatly affect the quality of the package. However, problems may arise in larger capacity operations and/or in machine structures wherein the contact rolls are loaded unevenly.
U.S. Pat. No. 4,106,710 proposes that a fork-shaped mount of a driving roll for contacting and rotating a yarn package should be supported on two diaphragm cylinders charged with compressed air, and that the desired pressure should be applied to the roll. These diaphragm cylinders have a complicated design, and they are pressed together as the diameter of the spool increases. This continuously raises the pressing pressure of the driving roll, until the mounting of the diaphragm cylinder is conducted radially away from the spool by means of a path sensor.
This known apparatus has the disadvantage that the pressing pressure of the contact roll is sensed only indirectly through the feed pressure of the diaphragm cylinders.